My Clown Pleco Is Neither Eating Algea Flakes Nor Cucumber!

I have 32G tank with only 1 clown pleco. Initially he was feasting on the algea in the tank.

I had cleaned the tank on the weekend. Now since there was no algea I was feeding him algea wafers. He didn't eat that for couple of days. Then I tried blanched cucumber. I boiled a slice in water for 2 min in microwave. It had shriveled a bit. I put that in the tank. He didn't eat that as well.

How did you clean tank? What is your maintenance schedule? The first thing I do when my fish are not acting normally is a water test: Ammonia, nitrite, nitrate. Once done I explore other possibilities.